Abstract
Abstract
Introduction
Examination of the on- and off-kinetic response of pulmonary oxygen uptake (VO2) allows evaluation of the efficiency of oxidative metabolism in skeletal muscle. Sympathetic nervous system hyperactivity and chronic intermittent hypoxemia associated with obstructive sleep apnea (OSA) may impair tissue oxygenation, thus limiting oxidative metabolism and exacerbating the onset of fatigue. Therefore, the present study aims to characterize VO2 kinetics during and after submaximal treadmill walking, and assess the degree of symmetry between on- and off-transients in adults with OSA.
Methods
Twenty-six volunteers (OSA: n=13, 47.5 ± 9.7years, BMI=29.3 ± 4.8kg/m2, AHI=46.7 ± 26.2; Non-OSA (NO): n=13, 40.5 ± 8.8years, BMI=23.8 ± 3.3kg/m2) performed three 6-minute bouts of submaximal exercise on treadmill, corresponding to 85% of anaerobic threshold (determined previously from a maximal exercise test). Indices of VO2 on- and off-kinetics include the time constant (τ) reflecting the rate of oxidative metabolism, VO2 amplitude (ΔVO2), and mean response time (MRT=time delay + τ). The transition constant (K=ΔVO2/MRT) reflects a normalized rate of VO2 kinetics. Apnea-hypopnea index (AHI) was captured for all OSA subjects. Data were compared using body mass index (BMI) as a covariate for ANCOVA.
Results
Both on- and off-transient τ and MRT did not differ between the groups (on-transient: OSA 33.7 ± 13.6s, NO 35 ± 11.8s, and OSA 50.6 ± 9.2s, NO 49.6 ± 8.9s respectively; off-transient: OSA 42 ± 21.1s, NO 38.6 ± 9.6s, and OSA 55.6 ± 20.7s, NO 49.9 ± 7.1s respectively). However, ΔVO2 and K for exercise and recovery were lower in OSA (on-transient: OSA 698 ± 289, NO 1075 ± 345mL/min, p=0.035 and OSA 13.8 ± 5.1, NO 21.8 ± 6.7mL/min/sec, p=0.01 respectively; off-transient: OSA 689 ± 285, NO 1047 ± 345mL/min, p=0.042 and OSA 12.9 ± 4.8, NO 20.9 ± 6.1mL/min/sec, p=0.007 respectively).
Conclusion
The VO2 kinetic responses during the on- and off-transients were symmetrical in both groups. The attenuated VO2 on- and off-kinetics in OSA suggests an impaired response of oxidative system to adjust to changing metabolic demand that may limit performance of daily-living tasks. The decreased physiological capacity to consume oxygen per unit time may have a significant implication for fatigue in this population.
Support (If Any)
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